HEAT/AC BLOWER NOT FUNCTIONING

1930 Mercedes Benz 300e

Heater problem
Mercedes Benz 300e 6 cyl Two Wheel Drive Automatic

Fuse checked: OK
suspect wither the pushbutton switch has failed; however, defrost (usually blows at the highest speed automatically) also DOES NOT get blower going.
Is there a relay involved, and where is it?
How do I test the five button control panel, and the three button fan speed control?
How do I change out the heater blower motor (recent minor noise)?
thanks